Macro for MD children ?

Hello. I've been macro/vegan in the past and am curious if there are certain foods that could help children afflicted with neuromuscular diseases. My 6 yr old grandson has muscular dystrophy. Because he'll soon be taking Prednisone to combat muscle weakness resulting from this terminal disease I wonder if there are any foods in particular which could restore balance while he's taking this steroid.

There are very few treatments to help him delay the progression of DMD, unfortunately corticosteroids seem to be a necessary evil.

I've not seen this answered anywhere I've looked so I thought someone here might have an idea to start.